U.S. Pat. No. 6,975,689 issued on 13 Dec. 2005, based on U.S. patent application Ser. No. 9/823,500 filed 30 Mar. 2001, and titled “DIGITAL MODULATION SIGNAL RECEIVER WITH ADAPTIVE CHANNEL EQUALIZATION EMPLOYING DISCRETE FOURIER TRANSFORMS” is incorporated herein by reference. U.S. Pat. No. 7,050,491 issued on 23 May 2006, based on U.S. patent application Ser. No. 10/271,386 filed 15 Oct. 2002, and titled “ADAPTIVE EQUALIZATION OF DIGITAL MODULATING SIGNAL RECOVERED FROM AMPLITUDE-MODULATED SIGNAL SUBJECT TO MULTIPATH” is incorporated herein by reference. These patents describe how discrete Fourier transform methods can be employed for the adaptation of channel-equalization filtering. Other methods have been employed for the adaptation of channel-equalization filtering. The inventions claimed herein concern the configuration of the synchrodyne apparatus and can be used with various ones of these methods for the adaptation of channel-equalization filtering.
U.S. Pat. No. 6,512,555 titled “RADIO RECEIVER FOR VESTIGIAL-SIDEBAND AMPLITUDE-MODULATION DIGITAL TELEVISION SIGNALS” issued 28 Jan. 2003 to C. B. Patel and A. L. R. Limberg. This patent describes digital synchrodyning procedures in which an intermediate-frequency 8VSB DTV signal is mixed with unmodulated carriers nominally at 0° and 90° phasings respective to pilot carrier to recover real and imaginary components of a complex baseband DTV signal. The imaginary component of the complex baseband DTV signal is lowpass filtered to develop an automatic frequency and phase control (AFPC) signal for controlling the oscillator circuitry generating the unmodulated carriers at 0° and 90° phasings respective to pilot carrier. The real component of the complex baseband DTV signal is processed for reproducing the baseband DTV signal used to modulate the radio-frequency carrier transmitted from a broadcasting station selected for reception. This bandpass tracker tracks the phase of the pilot carrier that the selected broadcasting station transmits, and tracking falters if the pilot carrier is suppressed. The pilot carrier is suppressed during certain sorts of multipath reception conditions, for example.
U.S. Pat. No. 5,479,449 titled “DIGITAL VSB DETECTOR WITH BANDPASS PHASE TRACKER, AS FOR INCLUSION IN AN HDTV RECEIVER” issued 26 Dec. 1995 to C. B. Patel and A. L. R. Limberg. This patent describes digital synchrodyning procedures in which an intermediate-frequency 8VSB DTV signal is mixed with unmodulated carrier nominally at 0° phasing respective to pilot carrier to recover a real baseband DTV signal. The IF 8VSB DTV signal is filtered with a narrow bandpass filter to extract pilot carrier which is mixed with unmodulated carrier nominally at 90° phasing respective to pilot carrier. This is done to develop an automatic frequency and phase control (AFPC) signal for controlling the oscillator circuitry generating the unmodulated carriers at 0° and 90° phasings respective to pilot carrier.
U.S. Pat. No. 5,715,012 titled “RADIO RECEIVERS FOR RECEIVING BOTH VSB AND QAM DIGITAL HDTV SIGNALS” issued 3 Feb. 1998 to C. B. Patel and A. L. R. Limberg. This patent describes digital synchrodyning procedures in which an intermediate-frequency QAM DTV signal is mixed with unmodulated carriers at 0° and 90° phasings to recover real and imaginary components of a complex baseband DTV signal. The QAM DTV signal has no pilot carrier. The AFPC signal for controlling the oscillator circuitry generating the unmodulated carriers at 0° and 90° phasings respective to pilot carrier is developed by lowpass filtering the product of the real and the imaginary components of the complex baseband DTV signal, in accordance with the Costas principle.
U.S. Pat. No. 5,809,088 titled “DIGITAL CARRIER WAVE RESTORING DEVICE AND METHOD FOR USE IN A TELEVISION SIGNAL RECEIVER” issued 26 Sep. 1998 to D. S. Han. This patent describes digital synchrodyning procedures in which an intermediate-frequency DTV signal is mixed with unmodulated carriers at 0° and 90° phasings respective to pilot carrier to recover real and imaginary components of a complex baseband DTV signal. The AFPC signal for controlling the oscillator circuitry generating the unmodulated carriers at 0° and 90° phasings respective to pilot carrier is developed by lowpass filtering the product of the real and the imaginary components of the complex baseband DTV signal, in accordance with the Costas principle. This bandpass tracker continues tracking even if the pilot carrier is suppressed, which can occur during certain sorts of multipath reception conditions. In DTV receivers in which the passband rolls off in the carrier region of the frequency spectrum, the pilot carrier may be undesirably suppressed owing to mistuning of the selective front-end circuitry of the DTV receiver.
In the ensuing mathematical descriptions of the operation of synchrodyning apparatuses in DTV receivers, ωC is the carrier frequency of the intermediate-frequency input signal that is to be synchrodyned to baseband, and ωS is the frequency of a particular component of the signal modulating the amplitude of that carrier frequency. AS is the respective amplitude of that component, and φS is the respective phase of that component respective to an arbitrary reference. Time is the variable t.
The operation of the synchrodyning apparatus in a prior-art DTV receiver can be one in which an intermediate-frequency input signal that is essentially a summation of AS cos [(ωC−ωS)t−φS] terms for various ωS recovered by an odd number of frequency conversions is multiplicatively mixed with a cos ωCt carrier to recover a real baseband signal and with a sin ωCt carrier to recover an imaginary baseband signal. The real baseband signal recovered by the synchrodyning apparatus in such a receiver is a summation of cos(ωSt+φS) terms, in accordance with distributed application of the cos A cos B=0.5 cos(A+B)+0.5 cos(A−B) trigonometric identity, followed by lowpass filtering to suppress the cos(A+B) terms. The imaginary signal recovered by the synchrodyning apparatus in such a receiver is a summation of sin(ωSt+φS) terms, in accordance with distributed application of the sin A cos B=0.5 sin(A+B)+0.5 sin(A−B) trigonometric identity, followed by lowpass filtering to suppress the sin(A+B) terms.
Alternatively, the operation of the synchrodyning apparatus in a prior-art DTV receiver can be one in which an intermediate-frequency input signal that is essentially a summation of cos [(ωC+ωS)t+φS] terms recovered by an even number of frequency conversions is multiplicatively mixed with a cos ωCt carrier to recover a real baseband signal and with a sin ωCt carrier to recover an imaginary baseband signal. The real baseband signal recovered by the synchrodyning apparatus in such a receiver is a summation of cos(−ωSt−φS) terms, in accordance with distributed application of the cos A cos B=0.5 cos(A+B)+0.5 cos(A−B) trigonometric identity, followed by lowpass filtering to suppress the cos(A+B) terms. The summation of cos(−ωSt−φS) terms is the same as a summation of cos(ωSt+φS) terms. The imaginary signal recovered by the synchrodyning apparatus in such a receiver is a summation of sin(−ωSt−φS) terms, in accordance with distributed application of the sin A cos B=0.5 sin(A+B)+0.5 sin(A−B) trigonometric identity, followed by lowpass filtering to suppress the sin(A+B) terms. The summation of sin(−ωSt−φS) terms is the negative of a summation of sin(ωSt+φS) terms.
In accordance with an aspect of the invention the synchrodyning apparatus in a DTV receiver is operated so that an intermediate-frequency input signal that is essentially a summation of cos [(ωC−ωS)t−φS] terms recovered by an odd number of frequency conversions is multiplicatively mixed with a cos [ωCt+(π/4)] carrier and with a cos [ωCt−(π/4)] carrier. Multiplication by the cos [ωCt+(π/4)] carrier generates a summation of 0.5 cos [ωSt+φS+(π/4)] baseband terms plus a summation of 0.5 cos [(2ωC−ωS)t−φS−(π/4)] image terms, in accordance with distributed application of the cos A cos B=0.5 cos(A+B)+0.5 cos(A−B) trigonometric identity. Lowpass filtering separates the 0.5 cos [ωSt+φS+(π/4)] baseband terms from the image terms to supply a first mixer output signal. Multiplication of the summation of cos [(ωC−ωS)t−φS] terms by the cos [(ωCt−(π/4)] carrier generates a summation of 0.5 cos [ωSt+φS−(π/4)] baseband terms plus a summation of 0.5 cos [(2ωC−ωD)t−φS−(π/4)] image terms, in accordance with distributed application of the cos A cos B=0.5 cos(A+B)+0.5 cos(A−B) trigonometric identity. Lowpass filtering separates the 0.5 cos [ωSt+φS+(π/4)] baseband terms from the image terms to supply a second mixer output signal. Summing the first and second mixer output signals generates, in accordance with the cos A+cos B=2 cos 0.5 (A+B) cos 0.5 (A−B) trigonometric identity, a summation of cos(π/4) cos(ωSt+φS) terms, reproducing the baseband modulating signal scaled by the factor 0.707. Differentially combining the first and second mixer output signals generates, in accordance with the cos B−cos A=2 sin 0.5 (A+B) sin 0.5 (A−B) trigonometric identity, a summation of sin(π/4) sin(ωSt+φS) terms that is the Hilbert transform of the baseband modulating signal scaled by the factor 0.707.
In accordance with another aspect of the invention, the synchrodyning apparatus in a DTV receiver is operated so that an intermediate-frequency input signal that is essentially a summation of cos [(ωC+ωS)t+φS] terms recovered by an even number of frequency conversions is multiplicatively mixed with a cos [ωCt+(π/4)] carrier and with a cos [ωCt−(π/4)] carrier. Multiplication by the cos [ωCt+(π/4)] carrier generates a summation of 0.5 cos [ωSt+φS−(π/4)] baseband terms plus a summation of 0.5 cos [(2ωC+ωS)t+φS+(π/4)] image terms, in accordance with distributed application of the cos A cos B=0.5 cos(A+B)+0.5 cos(A−B) trigonometric identity. Lowpass filtering separates the 0.5 cos [ωSt+φS−(π/4)] baseband terms from the image terms to supply a first mixer output signal. Multiplication of the summation of cos [(ωC+ωS)t+φS] terms by the cos [ωCt−(π/4)] carrier generates a summation of 0.5 cos [ωSt+φS+(π/4)] baseband terms plus a summation of 0.5 cos [(2ωC+ωS)t−φS−(π/4)] image terms, in accordance with distributed application of the cos A cos B=0.5 cos(A+B)+0.5 cos(A−B) trigonometric identity. Lowpass filtering separates the 0.5 cos [ωSt+φS+(π/4)] baseband terms from the image terms to supply a second mixer output signal. Summing the first and second mixer output signals generates, in accordance with the cos A+cos B=2 cos 0.5 (A+B) cos 0.5 (A−B) trigonometric identity, a summation of cos(π/4)cos ωSt+φS) terms, reproducing the baseband modulating signal scaled by the factor 0.707. Differentially combining the first and second mixer output signals generates, in accordance with the cos B−cos A=2 sin 0.5 (A+B) sin 0.5 (A−B) trigonometric identity, a summation of sin(π/4)sin(ωSt+φS) terms that is the Hilbert transform of the baseband modulating signal scaled by the factor 0.707.
Note that the 0.5 cos [(2ωC+ωS)t−φS−(π/4)] and 0.5 cos [(2ωC−ωS)t−φS−(π/4)] image terms are easier to suppress by lowpass filtering than 0.5 cos [(2ωC−ωS)t−φS−(π/4)] and 0.5 cos [(2ωC−ωS)t−φS+(π/4)] image terms are. Accordingly, there is reason for preferring an even number of frequency conversions of the received RF signal to develop the IF signal used for synchrodyning.